A law firm representing 343 residents of a Carson housing tract filed a lawsuit Wednesday against Shell Oil, alleging the company knowingly contaminated the neighborhood more than 40 years ago.

The lawsuit, filed in Long Beach Superior Court, alleges that residents have been harmed, and some have died, as a result of elevated levels of benzene in the Carousel neighborhood.

The benzene has been traced to a tank farm that Shell operated on the site from 1924 to 1967. Though testing is still under way, plaintiff’s attorney Tom Girardi said that preliminary results are alarming enough to move ahead with litigation.

“One thing we do know, Shell has wiped out 280 houses,” Girardi said. “I’ve handled cases like this for 40 years all over the country. We’ve never seen levels like this of contaminants.”

Shell began testing a few months ago in the neighborhood, which lies north of Lomita Boulevard between Panama and Marbella avenues. The results showed levels of benzene up to 100,000 times the state standard, as well as elevated levels of methane.

Once the results were made known, residents contacted environmental activist Erin Brockovich, who works with Girardi and Keese on contamination cases around the country.

The firm agreed to take the case, and signed up hundreds of clients after holding a community meeting.

The lawsuit targets Shell as well as Castle and Cooke, a real estate firm that bought out the developer of the Carousel tract, Barclay Hollander Curci.

In an interview, Girardi said as many as another 200 plaintiffs are expected to join the 343 who are already listed as plaintiffs in the lawsuit.

The suit claims that at least four residents died from exposure to contamination.

The Regional Water Quality Control Board is directing the remediation effort, which entails further testing on private property.

The board held a meeting last week, during which many residents expressed frustration with the process. Some residents have said they want to move, but are concerned about the loss in property values due to the contamination.

Others have said they are worried about having their children or grandchildren come for a visit.

“We know we have to get out for health reasons,” said Barbara Post, the president of the Carousel Homeowners Association.

Shell has asked for residents’ cooperation in the testing process, but many have refused to allow Shell’s geologists onto their property.

“We know that people want answers and we’re trying to get them answers,” said Alison Chassin, a Shell spokeswoman. “In order to do that, we need to take the samples.”

Girardi and Keese has advised its clients not to sign access agreements until the attorneys can provide their input.